At present, in the 3GPP (3rd Generation Partnership Project), a standardization association, the specifications of an LTE (Long Term Evolution) system and an LTE-A (LTE-Advanced) system based on the LTE system are studied. As to the LTE, LTE Release 8 to LTE Release 12 have been worked out as international specifications. LTE Release 10 or after is called LTE-Advanced, which is regarded as 4th generation mobile communication (4G).
In the LTE, for downlink transmission, OFDMA (Orthogonal Frequency Division Multiple Access) is used. Also, for uplink transmission, DFT-s-FDMA (Discrete Fourier Transform-spread Orthogonal Frequency Division Multiple Access) or SC-FDMA (Single Carrier-FDMA) are used. In the OFDMA, because subcarriers are orthogonal, causing no interference among the subcarriers, it is possible to prevent the occurrence of interference in data transmission between users (or between terminals) in a cell.
Meanwhile, the study of 5th generation mobile communication (5G) after 4G has been started from about the year 2013. As a technique to be introduced in 5G, Non-Orthogonal Multiple Access (NOMA) is under study. In the 3GPP, a study for introducing the non-orthogonal multiple access is to be started in order to establish the specification of the LTE Release 13 and after. As a non-orthogonal multiple access scheme, FTN (Faster-Than-Nyquist), FMBC (Filter Bank Multi Carrier) and Super Position Coding (hierarchical modulation) are also under study.
Such techniques related to radio communication include techniques as follows, for example. Namely, there is a method and an apparatus in which a user apparatus (UE), located in an expanded range area of an adjacent base station cell in a communication network, reports the UE capability of canceling interference from the transmission of another cell, to a serving base station such as a macro cell which includes a low power cell. According to the above technique, it is urged that the expansion of a range can be determined optimally and beneficially for both a homogeneous network and a heterogeneous network.
Further, there is a technique of setting a hierarchy ratio, which is a signal power ratio at the superposition of an upper layer with a lower layer, a mapping pattern capable of selecting two patterns from bit mapping pattern candidates with an allowed overlap, and a ratio of mixing two mapping patterns in a signal sequence, as hierarchal parameters. It is urged that, according to the above technique, a communication system capable of flexibly adjusting the quality of each link in hierarchical modulation can be obtained.
Further, there is a radio communication system in which N×n sets of propagation environment information, reported from n terminals, are aggregated and the scheduling is performed by integrating a plurality of different communication services into one, so that a terminal, having a satisfactory propagation environment over a plurality of different communication services, and a communication service to be provided to the terminal are selected. According to the above technique, it is urged that the scheduling performed by integrating a plurality of communication services into one enables improved operability in radio communication.
Further, there is a radio base station which selects a user terminal from each user group according to the channel gain of each user terminal, to determine a user set to be non-orthogonally multiplexed to an arbitrary radio resource using transmission power which is fixedly allocated to each user group. In this case, the radio base station transmits a downlink signal to each user terminal in the user set, using transmission power allocated to each user group. According to this technique, it is urged that link adaptation which is optimal for a future radio communication system can be achieved.
Moreover, there is also a radio base station which multiplexes downlink data for each of a plurality of user terminals on each sub-band basis, to perform transmission using transmission power allocated to each of the plurality of user terminals on each sub-band basis. According to this technique, it is urged that link adaptation suitable for a future radio communication system can be obtained.